Fix: Audio formats in Gstreamer plugin (#1107)

Sakoram · MateuszGrabuszynski · web-flow · commit 8afd40862ec4 · 2025-04-16T10:04:50.000+02:00
- Interpret PCM format as big endian in Gstreamer plugin
- Fix audio formats description in README.

---------

Signed-off-by: Kasiewicz, Marek &lt;marek.kasiewicz@intel.com&gt;
Co-authored-by: Mateusz Grabuszyński &lt;mgrabuszynski@gmail.com&gt;
diff --git a/ecosystem/gstreamer_plugin/README.md b/ecosystem/gstreamer_plugin/README.md
@@ -273,7 +273,7 @@ Audio plugins for MTL that are able to send, receive synchronous raw audio via t
 
 The `mtl_st30p_tx` plugin supports the following pad capabilities:
 
-- **Formats**: `S16LE`, `S24LE`, `S32LE`
+- **Formats**: `S8`, `S16BE`, `S24BE`
 - **Sample Rate Range**: 44100, 48000, 96000
 - **Channels Range**: 1 to 8
 
@@ -285,7 +285,7 @@ The `mtl_st30p_tx` plugin supports the following pad capabilities:
 | tx-ptime             | string  | Packetization time for the audio stream.              | `1ms`, `125us`, `250us`, `333us`, `4ms`, `80us`, `1.09ms`, `0.14ms`, `0.09ms` | `1.09ms` for 44.1kHz, `1ms` for others |
 | async-session-create | boolean | Improve initialization time by creating a session in a separate thread. All buffers that arrive before the session is ready will be dropped | TRUE/FALSE              | FALSE         |
 
-#### 4.1.2. Example GStreamer Pipeline for Transmission with s16LE format
+#### 4.1.2. Example GStreamer Pipeline for Transmission with s16BE format
 
 To run the `mtl_st30p_tx` plugin, you need to setup metadata (Here we are using pipeline capabilities).
 Instead of using input video we opted for build-in GStreamer audio files generator.
@@ -297,7 +297,7 @@ export VFIO_PORT_T="pci_address_of_the_device"
 
 # Audio pipeline with 48kHz sample rate on port 30000
 gst-launch-1.0 audiotestsrc ! \
-audio/x-raw,format=S16LE,rate=48000,channels=2 ! \
+audio/x-raw,format=S16BE,rate=48000,channels=2 ! \
 mtl_st30p_tx tx-queues=4 rx-queues=0 udp-port=30000 payload-type=113 dev-ip="192.168.96.3" ip="239.168.75.30" dev-port=$VFIO_PORT_T \
 --gst-plugin-path $GSTREAMER_PLUGINS_PATH
 ```
@@ -308,19 +308,21 @@ mtl_st30p_tx tx-queues=4 rx-queues=0 udp-port=30000 payload-type=113 dev-ip="192
 
 The `mtl_st30p_rx` plugin supports the following pad capabilities:
 
-- **Formats**: `S8`, `S16LE`, `S24LE`
+- **Formats**: `S8`, `S16BE`, `S24BE`
 - **Channels Range**: 1 to 2
 - **Sample Rate Range**: 44100, 48000, 96000
 
 **Arguments**
-| Property Name       | Type    | Description                                           | Range                   | Default Value |
-|---------------------|---------|-------------------------------------------------------|-------------------------|---------------|
-| rx-framebuff-num    | uint    | Number of framebuffers to be used for transmission.   | 0 to G_MAXUINT          | 3             |
-| rx-channel          | uint    | Audio channel number.                                 | 0 to G_MAXUINT          | 2             |
+| Property Name       | Type    | Description                                           | Range                    | Default Value |
+|---------------------|---------|-------------------------------------------------------|--------------------------|---------------|
+| rx-framebuff-num    | uint    | Number of framebuffers to be used for transmission.   | 0 to G_MAXUINT           | 3             |
+| rx-channel          | uint    | Audio channel number.                                 | 0 to G_MAXUINT           | 2             |
 | rx-sampling         | uint    | Audio sampling rate.                                  | [Supported Audio Sampling Rates](#232-supported-audio-sampling-rates) | 48000         |
-| rx-audio-format     | string  | Audio format type.                                    | `S8`, `S16LE`, `S24LE`  | `S16LE`       |
+| rx-audio-format     | string  | Audio format type.                                    | `PCM8`, `PCM16`, `PCM24` | `PCM16`       |
 | rx-ptime            | string  | Packetization time for the audio stream.              | `1ms`, `125us`, `250us`, `333us`, `4ms`, `80us`, `1.09ms`, `0.14ms`, `0.09ms` | `1.09ms` for 44.1kHz, `1ms` for others |
 
+> **Note**: The `PCM` formats are interpreted as big endian.
+
 #### 4.2.2. Preparing Output Path
 
 In our pipelines, we will use the `$OUTPUT` variable to hold the path to the audio file.
@@ -344,7 +346,7 @@ export VFIO_PORT_R="pci_address_of_the_device"
 export OUTPUT="path_to_the_file_we_want_to_save"
 
 # Run the receiver pipeline
-gst-launch-1.0 -v mtl_st30p_rx rx-queues=4 udp-port=30000 payload-type=111 dev-ip="192.168.96.2" ip="239.168.75.30" dev-port=$VFIO_PORT_R rx-audio-format=PCM24 rx-channel=2 rx-sampling=48000 ! \
+gst-launch-1.0 -v mtl_st30p_rx rx-queues=4 udp-port=30000 payload-type=111 dev-ip="192.168.96.2" ip="239.168.75.30" dev-port=$VFIO_PORT_R rx-audio-format=PCM16 rx-channel=2 rx-sampling=48000 ! \
 filesink location=$OUTPUT --gst-plugin-path $GSTREAMER_PLUGINS_PATH
 ```
 
diff --git a/ecosystem/gstreamer_plugin/gst_mtl_st30p_rx.c b/ecosystem/gstreamer_plugin/gst_mtl_st30p_rx.c
@@ -103,7 +103,7 @@ enum {
 static GstStaticPadTemplate gst_mtl_st30p_rx_src_pad_template =
     GST_STATIC_PAD_TEMPLATE("src", GST_PAD_SRC, GST_PAD_ALWAYS,
                             GST_STATIC_CAPS("audio/x-raw, "
-                                            "format = (string) {S8, S16LE, S24LE},"
+                                            "format = (string) {S8, S16BE, S24BE},"
                                             "channels = (int) [1, 2], "
                                             "rate = (int) {44100, 48000, 96000}"));
 
@@ -362,11 +362,11 @@ static gboolean gst_mtl_st30p_rx_negotiate(GstBaseSrc* basesrc) {
 
   switch (ops_rx->fmt) {
     case ST30_FMT_PCM24:
-      gst_audio_info_set_format(info, GST_AUDIO_FORMAT_S24LE, sampling, ops_rx->channel,
+      gst_audio_info_set_format(info, GST_AUDIO_FORMAT_S24BE, sampling, ops_rx->channel,
                                 NULL);
       break;
     case ST30_FMT_PCM16:
-      gst_audio_info_set_format(info, GST_AUDIO_FORMAT_S16LE, sampling, ops_rx->channel,
+      gst_audio_info_set_format(info, GST_AUDIO_FORMAT_S16BE, sampling, ops_rx->channel,
                                 NULL);
       break;
     case ST30_FMT_PCM8:
diff --git a/ecosystem/gstreamer_plugin/gst_mtl_st30p_tx.c b/ecosystem/gstreamer_plugin/gst_mtl_st30p_tx.c
@@ -109,7 +109,7 @@ typedef struct {
 static GstStaticPadTemplate gst_mtl_st30p_tx_sink_pad_template =
     GST_STATIC_PAD_TEMPLATE("sink", GST_PAD_SINK, GST_PAD_ALWAYS,
                             GST_STATIC_CAPS("audio/x-raw, "
-                                            "format = (string) {S8, S16LE, S24LE},"
+                                            "format = (string) {S8, S16BE, S24BE},"
                                             "channels = (int) [1, 2], "
                                             "rate = (int) {44100, 48000, 96000}"));
 
@@ -308,19 +308,21 @@ static gboolean gst_mtl_st30p_tx_session_create(Gst_Mtl_St30p_Tx* sink, GstCaps*
   }
   ops_tx.name = "st30sink";
   ops_tx.fmt = ST30_FMT_PCM16;
-  if (!info->finfo) {
-    ops_tx.fmt = ST30_FMT_PCM24;
-  } else {
-    if (info->finfo->format == GST_AUDIO_FORMAT_S24LE) {
-      ops_tx.fmt = ST30_FMT_PCM24;
-    } else if (info->finfo->format == GST_AUDIO_FORMAT_S16LE) {
-      ops_tx.fmt = ST30_FMT_PCM16;
-    } else if (info->finfo->format == GST_AUDIO_FORMAT_S8) {
-      ops_tx.fmt = ST30_FMT_PCM8;
-    } else {
-      gst_audio_info_free(info);
-      GST_ERROR(" invalid format audio");
-      return FALSE;
+  if (info->finfo) {
+    switch (info->finfo->format) {
+      case GST_AUDIO_FORMAT_S24BE:
+        ops_tx.fmt = ST30_FMT_PCM24;
+        break;
+      case GST_AUDIO_FORMAT_S16BE:
+        ops_tx.fmt = ST30_FMT_PCM16;
+        break;
+      case GST_AUDIO_FORMAT_S8:
+        ops_tx.fmt = ST30_FMT_PCM8;
+        break;
+      default:
+        gst_audio_info_free(info);
+        GST_ERROR(" invalid audio format");
+        return FALSE;
     }
   }
   ops_tx.channel = info->channels;
diff --git a/include/st30_api.h b/include/st30_api.h
@@ -97,6 +97,7 @@ typedef struct st_rx_audio_session_handle_impl* st30_rx_handle;
 
 /**
  * Payload format of st2110-30/31(audio) streaming
+ * Note: PCM format is interpreted as big endian.
  */
 enum st30_fmt {
   ST30_FMT_PCM8 = 0, /**< 8 bits per channel */
